Process and apparatus for vacuum distillation



July 22; 1930. P, SUBKQW 1,771,385

PROCESS AND APPARATUS FOR VACUUM DISTILLATION Filed Sept. 6, 1927 IN VEN TOR.

Patented Jul 22,1930

UNITED STATES PATENT OFFICE PHILIP sunxow; or Los menus, canmonnm,n'ssreron To UNION on. ooxrm or cans-01mm, or Los ANGELES, CALIFORNIA, aoonrou'rron or CALIFORNIA PROCESS AND APPARATUS FOR VACUUM DIBTILLATIONI Application filed September 8, 1927.- Serial 110. 217,781.

In vacuum distillation, the amount of vacuum which may be imposed on thevaporizing surface is determined in part by the back pressure of thevapor conduits and vaportreating means interposed between the vaporizingsurface and the vacuum generating means. The usual rectification orfractionating tower, wherein vapor is fractionated by repeatedcounter-current contacts with partial condensates from the vapor,usually imposes a back pressure on a vapor generating means which, inpart, nullifies the efliciency of the vacuum distillation, In mostfractionating columns of the bubble type, the back pressure per platemay be as much as 25 m. m. of mercury. It is not uncommon for afractionating column to be from 10 to 20 plates high. While ;filled typecolumns show a smaller back pressure, yet the total back pressure'of acolumn giving desired fractionating elli'ciencies will often be found tobe such that the backpressure thus imposed upon the vaporizing surfacelimits, to a very material degree, the amount of vacuum maintainablethereon. It is, therefore, well-known that fractionating columns can notbe employed in high vacuum distillations'. Such high vacuumdistillations have become of particular importance in the production oflubricating oils wherein the pressure at times may be less than 25 m. m.or range up to 200 or 300 m. m. Fractionating columns have not beenfound feasible at such'vacuum and the only means of fractionating thevapors, at the present time, is that of fractional condensation.

It is one of the objects of this invention to devise a rocess andapparatus for vacuum distillation wherein the vapors are rectified byrepeated counter-current contacts with partial condensates formed fromsaid mpors; that is rectified under such conditions that this does notlimit the degree of vacuum maintained on the vaporizing surface; i. e.under such conditions as would eliminate the back pressure of therectifying process or apparatus. Generically, this process comprisesgenerating vapors under the desired vacuum and fractionating the vaporsat succeedingly higher sub-atmospheric pressure; i. e. at succeedinglylower vacuums. by counter-current from said vapors.

contact which partial condensates produce It is another object of thisinvention to rectify vapors under vacuum wherein the rectificationcolumn functions both as a fractionating unit and as a vacuum pumpwhereby the vapors are compressed bodying the novel method ofdistillation and fractionation.

(1) is a furnace, (2) is a still, (3) ava or conduit, (4) a fractionatincolumn, (5) a condenser, (6) a condenser x, (7 a rundown tank, (8) aresidual vapor line, (9) a vacuum pump, (10) a vapor exhaust pipe.

The fractionatin column (4) is composed of a series of bublfie plates(11). Between the successive bubble lates are positioned imperforateplates (12 Downcomer (13) leads the liquid from one bubble plate to thenext lower bubble plate, and passes throughimperforate plate (12). The sace (21) above the bubble plate is connecte with the space (14) betweenthe imperforate plate (12) and the next upper plate (11) by means ofconduits (15) and (16) which are connected by means of pump (17).Conduit (15) is controlled by a valve (18) and conduit (16) iscontrolled by a valve (19). As will be seen, there isa pump (17)positioned between each bubble late and the next upper chamber (14) At te top of the tower (4) is a dephlegmating coil (20).

The operation of the device is as follows:

Vapor is generated in still (2) and passed through line (3) into thetower (4). The various pum s (17) are so operated by the regulation 0their speed and/or the regulation of the valves (18) and (19) thatsuccessive degrees of vacuum are produced. They would thus function toforce the vapors against the back pressure of the next upper plate andalso to cause successive stages of.

exhaust. Thus thevarious p mp (1 9 mm m desire vacuum 'in (2). Thesepumps (17) and pump (9 may be conceived of as successive stages onevacuum producing means,

producing successive higher compressions until the vapors are exhaustedinto the atmosphere or into the vapor collecting line (10) which may beat the desired pressure, as, for instance, when it is connected to avapor collecting line. While the drawing shows as many pumps as thereare plates, if

will be understood that one pump may func' tion for two or more plates.Thus vapor may pass through two or three or more lates counter-currentto downcoming liqui and then into asta-ge ofvacuum, i. e., a vacuumpump, to be compressed to pass through a succeeding number of plates;then into another stage of vacuum, 1. e., a vacuum pump, and so on untilit passes into the final condenser. This is a matter of design dependingon the capacity of the pumps and the back pressure of each section ofthe tower. Thus the fractionating column operates at succeedingly higherpressures to produce fractiona tion and, at the same time, the vaporsare exhausted at successive stages to be fractionated betweencompressions. In this manner, no one pump must bear the brunt of all theexhausting action, and the regulation of fractionation and distillationis made easier. It .is obvious that the pumps and tower will be welllagged to prevent heat losses.

As an example of one method of application, suppose distillation is tooccur at 25 m. m. pressure and vapo'rs are to be exhausted toatmosphere. Assuming that the back pressure of the condensing unit isequal to m. m., the amount of vacuum, which must be generated by theseveral pumps of the fractionating column, is equal to approximately 685m. m. If the fractionating column is composed of ten stages of vacuum,i. e. ten vacuum pumps, each pump must generate approximately 68.5 m. m.vacuum. It is obvious that a different proportioning of the amount ofvacuum generated by the various pumps may be obtained. Thus, since thevolume of vapor decreases upwardly through the column, the upper pumpsmay operate to generate greater vacuum than the lower exaust pumps. Itwill be observed here that the back pressure of the fractionating columnmay be and probably will be much less than 685 In. m. and that,therefore, the vacuum generating means associated with the fractionatingcolumn may generate much more i than the compression necessary toovercome the back pressure of the column. The column functions as avacuum generating means as well as a fractionating or rectifying column.However, should the back pressure of the column just equal or be greaterthan 685 m. m., the pumpswill function to overcome this back pressureand ensure the maintenance of the high vacuum in the still and cause anexhaust of the vapors, at successive stages with a parallelrectification. While the specific embodiment shows the pumps positionedoutside the column and connected thereto by relatively long vapor lines,the pumps may be positioned insidethe column or positioned adjacent tothe column in a manner described in co-pending applications Serial Nos.217,789 and 217,790, filed September 6, 1927.

The above description is not to be taken as limiting my invention, butmerely descriptive of the best manner of carrying it out, my inventionbeing described in the following claims, in which I claim:

1. The process of rectification in vacuum which comprises contactingvapors with partial condensates in successive stages at increasingsub-atmospheric pressure.

2. The process of rectifying vapors in vacuum which comprises passinsaid vapors into counter-current contact with partial condensatesproduced from said vapors in a plurality of stages and maintaining thesuccessive stages at increasing sub-atmospheric pressures.

3. The process of rectifying vapors in vacuum which comprises passingsaid vapors into contact with a partial condensate produced from saidvapors, withdrawing said vapors, compressing said vapors to a pressureless than atmospheric, introducing said c0mpressed Vapors intocounter-current contact with a partial condensate produced from saidvapors, withdrawing the va-pors resulting from the last mentionedcounter-current and finally condensing said vapors.

4. The process of rectifying vapors in vacuum which comprises passingsaid vapors into counter-current contact with a partial condensateproduced from said vapors in a rectification column, compressing saidvapors at a plurality of points in said column to produce an increasingpressure in, the direction of flow of vapors through said column andmaintaining the pressure through said column at less than atmospheric.

5. The process of rectifying Vapors which comprises introducing saidvapors at sub-atmospheric pressure into a rectification column,withdrawing vapors from a portion of the tower, compressing said vaporsto a higher sub-atmospheric pressure, introducing said compressed vaporsinto said tower at a point adjacent to their point of withdrawal tocause rectification at higher sub-atmospheric pressures.

6. .The process of distillation which comprises vaporizing a liquid atsub-atmospher- 1c pressure, fractionating the vapors at succeedinglyhigher sub-atmospheric pressures but at pressures higher than in thevaporizing means and finally condensing said vapors.

7. The process of distillation, which comprises vaporizing vapors in avaporizing means at sub-atmospheric pressure, fractionatmg' the vaporsin a fractlonating means at succeedlngly higher sub-atmosphericpressures but at pressures higher than in the 6 vapor1z1ng means,maintaining the pressure gradient across said fractionating means.greater than the frictional resistance of said ractlonatmg means, andfinally condensing sa1d vapors. v m SIgned at Los Angeles, in the countyof Los Angeles and State of California, this 31st day of August, A. D.1927. j PHILIP SUBKOW.

cniuncm or coanncnon.

Patent No. 1, 771,385. Granted July 22,1930, to

PHILIP SUBKOW.

'It is hereby certified that error; appears in theprinted specificationof the above numbered patent requiring correction as follows: Page 2,line 11, for "if" *read it;-.'same page, line 100, claim 3,after""vap0rs" first occurrence, insert the words "to cause said contactat a pressure higher than during the first mentioned "contact"; line 122; claim 5, for "pressures" read'p'ressure; and that the said-LettersPatent should be read withthese correctionstherein that the same maycouformto the record of the casein the Patent Office.

Signed and sealed this 9th day of September, A. D. 1930.

L Y biQJtMoore, (Seal) I Actingfionnnissioner of Patents.

